The present invention relates generally to an automatic tension control device for regulating the amount of tension under which a filamentary material is withdrawn from a spool. More particularly, the present invention relates to such a tension control device which tends to maintain substantially constant tension in filamentary materials over variances in operating parameters. More specifically, the present invention relates to such a tension control device which employs a suspended spindle operative with a band brake assembly, thereby tending to maintain substantially constant tension in a filament.
Filamentary materials include fibers in single and multiple strands, flat bands, or tubing produced in long lengths and conveniently wound on spools. The various filamentary materials may be either natural or synthetic fibers, glass or metal. Such materials are commonly utilized as reinforcements for plastic or elastomeric compounds or may themselves be fabricated into integral items as in the textile industry. Regardless of the application, it is customary to withdraw the filamentary material from the spool at or near the location it is being used. To facilitate such removal, the spool is customarily mounted on a spindle or let-off device which permits the spool to rotate as the filament is withdrawn.
Because payout of the filament from the spool may be at a high linear velocity, thereby imparting substantial momentum to the spool and related spindle mounting components, it is necessary to dissipate force rapidly in the event the filament breaks or the take-up velocity suddenly decreases. In either situation, filament tends to be payed out more rapidly than it is needed until rotation of the spool can compensate. Obviously, the problem is greatly multiplied when a creel assembly carrying up to several hundred spools is being used. Numerous braking devices have been developed for use with creels. Many of these provide for the filament to be payed out under tension greater than what is required for payout from the spool. As the tension decreases, with slack in the filament, the braking force is applied to slow the rotation of the spool. Further, the amount of tension to be maintained in the filament must be variable in order to accommodate operations with different filaments under various conditions. In the past, such creels having variable tension control have often required multiple individual adjustments and have not been desirably compact. Some designs have even required tension adjustments during payout of the filament, as the spool is emptied. In other instances, creels have exhibited undesirable hunting or loping in the form of periodic variations about a desired tension, particularly in high-tension applications.
One of the more commercially successful tension control devices used in the tire industry is in accordance with Applicant""s U.S. Pat. No. 3,899,143. That device has a support structure which carries a spool support and a separately mounted rotatable pivot shaft. A first lever arm fixed on the pivot shaft carries a guide for tensioning the filamentary material as it is withdrawn from a spool mounted on the spool support and a brake which selectively engages the spool support. A second lever arm fixed on the pivot shaft is operatively connected with an air cylinder which effects a biasing that is transmitted to the first lever arm via the pivot shaft.
Tension control devices according to U.S. Pat. No. 3,899,143 have demonstrated exemplary operating characteristics under a variety of conditions and with a variety of filaments. However, there are several situations in which these tension control devices are not well suited. It has been found that the control arm and guide roller are vulnerable to damage from over-tension possibly caused by entanglement of the spooled material. In instances where the filamentary material is a heavy gauge wire, the guide roller imparts a xe2x80x9ccastxe2x80x9d or distortion to the shape of the wire. This may lead to a less than satisfactory end product or the need to provide additional manufacturing equipment to straighten the wire. To the present time, there has been no comprehensive device for dispensing heavy filamentary material from a spool. Yet a third problem is that the control arm and roller inhibits closely mounting the multiple tension controllers on the creel assembly.
One way to overcome the foregoing problems associated with the prior art is to provide a tension control device in which the spool is carried by a pivotably mounted spindle assembly that is moveable with a pivotably mounted braking assembly. By utilizing a fixed cam that engages the braking assembly, the rotation of the spindle is inhibited whenever a predetermined tension force is absent from the filamentary material. The braking assembly is provided with a slidable block with cam bearings that are spring-biased against a curvilinear cam surface provided by the cam. This provides a gradual yet firm application or removal of a braking force depending upon the amount of tension applied to the filamentary material. The braking force, applied through the cam, adjusts in response to the varying tension of the material as it unwinds from the spool. An increasing tension accordingly acts on the pivotably mounted spindle assembly causing the braking force to be relieved by an increasing amount, thereby tending to keep the filament in constant tension; conversely, a decreasing tension causes a greater braking force to be applied, with full braking (within the limits of the device) at zero tension.
It is, therefore, an object of the present invention to provide a tension control device for filamentary material which provides for payout of a filamentary material at a uniform tension selected from a substantial range, irrespective of the rate at which the filament is taken up. It is another object of the present invention to provide such a tension control device which maintains substantially uniform tension on the filamentary material during payout, irrespective of the amount of filamentary material remaining on a spool. It is a further object of the present invention to provide such a tension control device which is relatively compact and readily adjusted so as to accommodate various heavy filamentary materials.
It is yet another object of the present invention to provide a tension control device for filamentary material which may be selectively loaded by a loading device to provide any desired tension setting over an operating range covering the applications for a particular device constructed according to the invention.
It is a further object of the present invention to provide a tension control device that does not impart a distortion to the filamentary material as it is withdrawn from a spool. It is still another object of the present invention to provide a predetermined threshold to the loading device which applies a braking force to the rotation of the spool which is overcome by a tension force applied by the filamentary material.
It is another object of the present invention to provide a tension control device in which the spool is carried by a pivotably mounted spindle assembly that is movable with a pivotably mounted braking assembly. It is still another object of the present invention to provide a fixed cam that engages the braking assembly and inhibits rotation of the spindle assembly whenever a predetermined tension force is absent from the filamentary material. A further object of the present invention is to provide the braking assembly with a slidable block with cam bearings that are spring-biased against a curvilinear cam surface provided by the cam to provide a gradual yet firm application or removal of braking force. It is still another object of the present invention to construct the interrelationship between the cam and the braking assembly so that as the tension force acting on the spindle changes, the braking force applied to the spindle changes, thereby tending to keep the filament tension constant.
It is still another object of the present invention to provide such a tension control device which may be combined with a plurality of such devices wherein the tension setting for the devices may be readily varied remotely by a single adjustment.
It is yet an additional object of the present invention to provide a tension control device, as described above, except wherein the fixed cam and brake shoe are replaced by a friction band brake assembly. It is still another object of the present invention to provide pivotable movement of the spindle assembly to allow for engagement by the friction band with varying applications of a braking force. As in the first embodiment, the spindle assembly is selectively loaded so as to initially exert a braking force on the spindle assembly.
It is yet another object of the present invention to assist the selectively loaded force by positioning the ends of the friction band so that each end is a different distance from the spindle assembly""s pivot point. It is still another object of the present invention to set the different distances of the braking band such that as tension is applied to the filamentary material, the tension forces overcome the loading force and the spindle moves to a position less restricted by the friction band and rotates. Accordingly, as the tension applied to the filamentary material is reduced, the spindle assembly rotates into a position where a larger amount of braking force is applied and rotation of the spool is reduced. It is still an additional object of the present invention to provide such a tension control device, wherein one end of the band is adjustable to change its distance from the center of the pivotably mounted spindle assembly.
It is yet another object of the present invention to allow for spring-biasing of the band""s ends to accommodate spindle movement during payout of the filamentary material and ensure more uniform withdrawal thereof.
It is still yet another object of present invention to preferably spring-bias the adjustable end, although the fixed end could also be spring-biased separately or together with the adjustable end.
At least one or more of the foregoing objects of the present invention, together with the advantages thereof over existing and prior art forms of filament tension control devices which will become apparent from the following description, are accomplished by the invention hereinafter described and claimed.
In general, the present invention contemplates a self-compensating tension control device for regulating the payout of filamentary material from a spool, comprising a fixed support, a spindle assembly pivotably mounted to the fixed support, the spindle assembly rotatably carrying the spool of filamentary material, wherein a pull-off force imparted by the filamentary material causes angular movement of the spindle assembly and rotation of the spool, and a braking assembly mounted to the fixed support and coupled to the spindle assembly, wherein the amount of braking force applied by the braking assembly corresponds to an angular position of the spindle assembly.